Had a Weaver K8 (8x) back in the 70s which had "fine" crosshairs but no longer remember if there was an "F" in the designation, or not.

I'm still a fan of the 1.5, 2.5, 3x and even 4x scopes with the POST and crosswire reticle, and still have some on some of my deer rifles.

The old stuff is not up to the optical quality of modern stuff, but then neither are my eyes anymore, so ...Weavers (including ones marked JC Higgins) have been doing a good job for me for well over 50 years and they show no signs of quitting now,

Look at the markings on the adjustment knobs, a lot of the old scopes, especially lower powered ones have 1/4" adjustments not 1/8" high power scopes were more target oriented and often had the finer adjustments.

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All else being equal (and it almost never is) bigger bullets tend to work better.

I think the K-types had 1/4 inch adjustments.
The T-types have 1/8 inch adjustments and came with target turrets you can add.
I have four T-36 with the target dot fine crosshairs on my target .22 LR rifles and have been using them for at least 10 years.
The target turrets are great when you shift from 50 to 100 yards targets quickly.

My first hunting scope was a K 2.5 and it was mounted on my first centerfire rifle, a customized Savage 110 that I used for varmint hunting and deer hunting. I shot lots of woodchucks with it, using handloaded 125 grain Sierra varmint bullets. My fartherst kill was a woodchuck at 450 yards, on the (second shot).

The Weaver scope was pretty nice and I don't remember much about optical quality, but it seemed fine to my late-teen eyes (wearing glasses).

I once read an article that tested the accuracy of pointing of various scopes, open iron sights, and receiver sights mounted on the same board, all set on a variable tripod and verified by a very high-powered target scope.

Result of the test showed a large difference in pointing accuracy between open irons and receiver sights, then a huge difference between the irons and a 2x scope. However, there was very little pointing error among the scopes.

Recognizing the value of scopes on a rifle, I've always hunting with them. After the 2.5x Weaver, about all my sporter scopes have been variables in the 3x-9x range.

If I could only have a single-powered scope, it would probably be a 4X, which was quite popular when variables weren't either available or affordable.

The highest power on all my scopes is used for sighting-in and spotting antlers, etc., but for walking around, at the lowest settings. On stand, I set them at about 6x, which allows adequate identification and reasonably quick shots. When time is available, power is turned up to spot antlers, etc. especially at the longest ranges (300 yards and up).

When walking around, scopes are set at their lowest power, for maximum field of view. I don't often walk around in deep woods with a scoped rifle, unless there are opportunities to take a stand in a fairly open area of mature trees.

The specifications on the K-10 that I have are:
made between 1950-1984
10 power
3-5 inch eye relief
12 foot field of view at 100 yards
1 inch tube
eye piece diameter 1.445 inch
front end diameter 1.550
length 15 and 7 sixteenths inches
weight 14 ounces
type of adjustment 1 quarter inch click
The type of cross hairs that came with it are conventional cross hairs, cross hairs with a center dot, and a range finder cross hairs with two horizontal hairs that cover 6 inches between hairs at 100 yards. I don't see anything specifically about what the F on your scope stands for.
All this information comes from the book Old Gunsights and Rifle Scopes Identification and Price Guide. It lists your scope value at $150-$250 but, like anything, the prices are subject to what its worth to the buyer.

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